android - 如何使用 Instagram 的 "TextLayoutView"改进 Android 上的 TextView 渲染

Question

为了改进 Instagram 中的 TextView 渲染，Instagram 的工程师在 here 中提供了一个 hack ，他们使用自定义 View (TextLayoutView)来缓存text.Layout，但是在这篇文章中，他们没有给我们演示或告诉我们如何使用它，所以如果我想使用这个hack，我该怎么做？

Answer 1

这是我的简单实现:

TextLayoutView:

public class TextLayoutView extends View {

private Layout mLayout;

public TextLayoutView(Context context) {
    this(context, null);
}

public TextLayoutView(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
}

public TextLayoutView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    setFocusable(true);
}

@Override
protected void onDraw(Canvas canvas) {
    long t1=System.currentTimeMillis();
    super.onDraw(canvas);
    canvas.save();
    if (mLayout != null) {
        canvas.translate(getPaddingLeft(), getPaddingTop());
        mLayout.draw(canvas);
    }

    canvas.restore();
    long t2=System.currentTimeMillis();
    Log.i("TEST", "onDraw::"+(t2-t1));
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    long t1=System.currentTimeMillis();
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    if (mLayout != null) {
        setMeasuredDimension(
                getPaddingLeft() + getPaddingRight() + mLayout.getWidth(),
                getPaddingTop() + getPaddingBottom() + mLayout.getHeight());
    }
    long t2=System.currentTimeMillis();
    Log.i("TEST", "onMeasure::"+(t2-t1));
}


public void setTextLayout(Layout layout) {
    mLayout = layout;
    requestLayout();
}}

你可以这样使用它:

    @Override
public View getView(int position, View convertView, ViewGroup parent) {
    ......
    viewHolder.textView.setTextLayout(getLayout(mList.get(position)));
    return convertView;
}
    private final Map<String, Layout> mLayoutMap = new ConcurrentHashMap<String, Layout>();
private Layout getLayout(String str) {
    Layout layout = mLayoutMap.get(str);
    if (layout == null) {
        TextPaint textPaint = new TextPaint();
        textPaint.setTextSize(20);
        layout = new StaticLayout(str, textPaint, width, Alignment.ALIGN_CENTER,
                1.0f, 0.0f, true);
        mLayoutMap.put(str, layout);
    }
    return layout;
}